"Spanish Jews once constituted one of the largest and most prosperous Jewish communities in the world."
In biblical days, the land of Tarshish was in the Iberian Peninsula, later to be called Spain. It was well known to the Jews.Nadene Goldfoot
Unmerciful riots and even pogroms started in 1391 in Spain against Jews, causing half of the Jewish population to be forcibly converted. More than 200,00 Jews went through a conversion process. 40,000 to 100,000 had already been expelled. This was an outgrowth of Christianity's growth and definition, who must have felt they were in political competition with Judaism, and decided to put an end to their Jewish population.
On March 31, 1492, the Spanish monarchs announced their Alhambra Decree which said that Jews would be expulsed from Castile and Aragon. They had to be out of Spain by July 31, 1492. Some moved to Portugal, where they would be able to live for a little while until that monarch decided to join Spain and expelled Jews there as well. This brought about the division of Jews into Ashkenazi and Sephari lines.
It was August 3, 1492 that the Italian, Christopher Columbus sailed with his 3 ships, the Nina, Pinta and the Santa Maria for India. This was 3 days after the expulsion of all Jews. He arrived in the New World off North America instead on October 12, 1492. It's thought that he was one of the Conversos, since he wrote letters to his son in Hebrew, a language not many were versed in unless they were Jewish. Some of his crew members had to have been Jews, needing to get out of the country. At the time, gambling on a sailing ship could have meant certain death. It was a frightening experience. Columbus had raised the money needed to make this journey by going to the Spanish monarchs for it. They were willing to gamble that he would bring back riches enough to put their money in the profit zone.
Mohammad had been born in 570 CE and died in 632 CE. It was also a proselytizing religion, so by the 8th Century CE, had spread out and overtook Spain's Iberian Peninsula. Already living there since the Romans had come into Israel were Jews, and the native Spaniards respected them as "People of the Book." The Muslim Moorish rulers were very tolerant of the Jews. When the Umayyad Caliphate fell in 750 CE, things rapidly changed for Jews. As conditions became horrid for the Jews, many converted and then were called Conversos, New Christians, or Marranos, an ugly term. Today people from this group are called a Hebrew word, Anusim. They have researched their ancestor's religion and many are now converting back to Judaism.
Ashkenazis were Jews who had left Israel in 70 CE when the Romans took Jerusalem and burned down the Temple and city, as the Sephardi had also, but Ashkenazis were the group that headed towards Rome, either by force or by choice, and then had gone into France and Germany. From there after many years, they found that by necessity they needed to leave and meandered into Eastern Europe, where they wound up on Poland and Lithuania, etc. in what was called the Pale of Settlement.
The distance in 70 CE from Jerusalem to Spain was much closer, and for reasons known to their leaders, that's the direction this Sephardic group had taken. Reasons could have been that the area was known to certain leaders who had the experience of travel and of trading in these places. The 2 groups stayed in communication with each other throughout the centuries.
What developed from 1492 was the Spanish Inquisition, which of course had already started before this date in the late 1300s.